Never sign up to a guild website!
It should go without saying that signing up to any "fansite" is a terrible idea, but a lot of people fail to realize how dangerous it is to sign up to any website regarding the MMO you're playing currently.
Think of this, how many people use the same password for everything? Ask yourself, how secure am I doing so?
Fact is, that if you sign up to any guild website anywhere, regardless of the MMO, you're handing them your email address right off the bat, an email address that, 9 times out of 10, is the same one used to create your game account. Then, if you happen to be using the same password for everything, you've effectively handed them your complete login details. This not only allows them to steal your hard earned gear and zeny, but allows them the ability to delete your characters.
Sadly, even if you happen to be using different passwords, the danger doesn't end there. Signing up to a guild site allows them access to your ip address, allowing them to discover your exact, real world, location with very little effort on their part. Opening yourself up to new level of harassment. If you didn't know, we have players on these very forums that were targeted with real world harassment, and were forced to move and hide their identity in order to escape such activities. People literally called said person day and night, and even left letters in their mailbox detailing how they would rape and murder them.
If you think that's bad, people can go even further to harm you. Knowledge of your email address allows them ability to look up your social media accounts and the like opening you up to a great deal of dangers you don't expect. There have even been cases on World of Warcraft where people have gone so far as to commit credit card fraud, literally targeting people they don't like, signing them up for a credit card then driving them into debt using little more than the information they've obtained through social media and their guild site.
So remember, use common sense, guard your privacy, your well being depends on it! Especially so in this community, full of hatred, scammers, gold sellers, and ne'er do wells!
The last one was removed because certain people decided to turn it into a personal attack, I'd ask that they don't do so again.